International patent publication WO 02/069030 published 6 Sep. 2002 and international patent publication WO 03/077013 published 18 Sep. 2003, both of which are incorporated by reference herein, disclose displays which have a modulated light source layer and a modulated display layer. The modulated light source layer is driven to produce a comparatively low-resolution representation of an image. The low-resolution representation is modulated by the display layer to provide a higher resolution image which can be viewed by an observer. The light source layer may, comprise a matrix of actively modulated light sources, such as light emitting diodes (LEDs). The display layer, which is positioned and aligned in front of the light source layer, may be a liquid crystal display (LCD).
If the two layers have different spatial resolutions (e.g. the light source layer's resolution may be about 0.1% that of the display layer) then both software correction methods and psychological effects (such as veiling luminance) prevent the viewer from noticing the resolution mismatch.
Electronic systems for driving light modulators such as arrays of LEDs or LCD panels are well understood to those skilled in the art. For example, LCD computer displays and televisions are commercially available. Such displays and televisions include circuitry for controlling the amount of light transmitted by individual pixels in an LCD panel.
The task of deriving from image data signals to control a light source layer and display layer can be computationally expensive. Deriving such signals can be executed by a processor of a computer's video/graphics card, or by some other appropriate processor integral to a computer, to the display itself or to a secondary device. Performance limitations of the processor can undesirably limit the rate at which successive image frames can be displayed. For example, if the processor is not powerful enough to process incoming video data at the frame rate of the video data then an observer may detect small pauses between successive frames of a video image such as a movie. This can distract the observer and negatively affect the observer's image viewing experience.
There is a need for practical, cost effective and efficient systems for displaying images on displays of the general type described above.